For a long while, I used to have reasonable rankings (as not much SEO / link-building was done), but 3 days ago, my rankings for all keywords have dropped sharply (see attached an example of some keywords, but the same has happened to other 100s of keywords that I am following).

In my Google Webmaster account, all seems to be normal. No signs of malware detection or anything of the kind.

At the same day that the rankings have dropped, an SEO firm has started doing some articles link-wheel to help push the rankings up a little. Although it has happenned at the same time, I find it hard to believe that this has caused it, since if it has caused it, I will ask the SEO firm to do the same to my competitors, right?

Another thought I had is about my pages being too much SEO optimized for a certain keyword which is: 1. in the name of the html page, the html title, description, H1, repeats 3 times in the article etc... and now I even build links with the same keyword to the page.

But if this is true, why Google has waited for more than half a year before deciding to "punish" me for being so SEO oriented.

Or maybe it just let me enjoy some grace in the first 6 months of my site being up and then, after seeing there are almost no links pointing at this site, it decided to drop the rankings...

any idea what has changed in the new Panda algorithm or what changes do I need to do on my side to recover from this?

Also: do you find my pages to be too much SEO optimized? (with each page being optimized to a keyword that appears: 1.) in the page name (url), 2.) In the title tag 3.) in the description tag 4.) in H1 5.) 3 times along the text) - is this too much?